Copolymers of olefins or of olefins and non-conjugated dienes with unsaturated derivatives of cyclic imides

ABSTRACT

Novel amorphous copolymers of mono-olefins or of mono-olefins and non-conjugated dienes with unsaturated derivatives of imides are disclosed. These copolymers containing from 99.9 to 80% by weight of non-polar units derived from at least two mono-olefins containing 2 to 18 carbon atoms, particularly ethylene and propene or ethylene and butene-1, and possibly one or more non-conjugated dienes, and from 0.1 to 20% units derived from an imide having the formula ##STR1## wherein Z is an alkenyl radical containing 2 to 16 carbon atoms, and 
     A designates a saturated or unsaturated divalent hydrocarbon radical which contains 2 to 12 carbon atoms and which may possibly carry amino, halogeno or carboxyl groups. 
     Some of said copolymers may be used as polymer additives in lubricating compounds to improve their viscosity index and to disperse the slurry which they may contain.

The present invention relates to substantially amorphous novelcopolymers of olefins or of olefins and non-conjugated dienes withunsaturated derivatives of cyclic imides. It also relates to thepreparation of said copolymers as well as to the utilization of some ofsaid copolymers as polymer additives for lubricating oils.

The copolymers according to the invention are substantially amorphousand contain from 99.9 to 80%, and preferably from 99.9 to 85% by weightof non-polar units derived from at least two mono-olefins containing 2to 18 carbon atoms, and possibly one or more non-conjugated dienes,wherein the proportion of said diene or dienes in the copolymer is loweror equal to 20% by weight, and from 0.1 to 20%, preferably 0.1 to 15%polar units derived from one or more cyclic imides having the formula:##STR2## where: Z represents an alkenyl radical having 2 to 16 carbonatoms, and,

A is a saturated or unsaturated divalent hydrocarbon radical containing2 to 12 carbon atoms, which radical A may possibly carry amino, halogenoor carboxyl groups.

The mono-olefins containing 2 to 18 carbon atoms from which derive thewhole, or only a part, of the non polar units may be advantageouslyalpha-olefins of the formula R--CH ═CH₂, where R designates hydrogen oran alkyl, aryl, aralkyl or alkaryl group having 1 to 16 carbon atoms,and particularly ethylene, propene, butene-1, pentene-1, hexene-1,methyl-4 pentene-1, octene-1; ethylene associated with an alpha-olefinhaving 3 to 6 carbon atoms, mainly propene or butene-1, is preferablyused.

The non-conjugated dienes, from which up to 20% by weight of thecopolymer units may possibly derive, can be linear or cyclic and may beselected particularly from the group comprising 1,4-hexadiene,methyl-2pentadiene, 1,4-cyclopentadiene, 1,5-cyclooctadiene,tetrahydro-4,7,8,9-indene, bicyclo-[3,2,0]-heptadiene-2,6,dicyclopentadiene, alkalidene-5-norbornene-2 such as, for instance,methylene-5-norbornene-2 and ethylidene-5-norbornene-2

The N-alkenylated cyclic imides hereinabove defined from which the polarunits of the copolymers according to the invention derive, are moreparticularly such as in the above indicated formula the alkenyl radicalZ linked to the nitrogen atom contains 2 to 8 carbon atoms and presentspreferably the unsaturation in the ω position relative to the nitrogenatom which it is linked to.

As examples of unsaturated cyclic imides which may produce the polarunits of the copolymers according to the invention, may be mentioned, ina non-limitative way, those N-alkenylated derivatives of the imideswhich are selected from the group comprising succinimide, glutarimide,maleimide, citraconic imide, phthalimide, the imide of himic anhydride,hexahydrophthalimide and the imides of tricarboxylic butane acid and ofthe esters of that acid, and particularly the N-vinylsuccinimide,N-allylsuccinimide, N-butenylsuccinimide, N-vinylmethyl-2 succinimide,N-vinyldimethyl-2,3 succinimide, N-vinylglutarimide, N-vinylmaleimide,N-vinylphthalimide, N-vinylcitraconimide, N-vinylhexahydrophthalimide,the N-vinyl imide of himic anhydride and the N-vinyl imide oftricarboxylic butane acid or the esters of that acid.

The copolymers of the invention may be substantially linear copolymerswith a random distribution of the units which they are composed of, oralso graft-copolymers wherein the units deriving from the cyclicunsaturated imides form hanging chains linked to a skeleton constitutedby an amorphous random copolymer of the mono-olefins or of themono-olefins and the non-conjugated diene or dienes forming thenon-polar units.

The random copolymers are prepared by coordination catalysis throughcontacting, in a suitable liquid medium at a temperature between -80° Cand +150° C, at least two of the above-mentioned mono-olefins andpossibly one or more non-conjugated dienes, with at least one of theunsaturated imides previously defined, used in the form of a complexwith a Lewis acid, in the presence of a catalytic system formed by theassociation of an organometallic compound of one or more elements ofclass I, II or III of the Mendeleev Periodic Table with a compound of atransition metal of classes IV to VIII of said Periodic Table, until acopolymer is formed.

The unsaturated imides from which the polar units of the randomcopolymers derive are engaged in copolymerisation with the mono-olefins,and possibly with the non conjugated dienes, in the form of complexeswith Lewis acids. A Lewis acid is any compound which may have thefunction of an acceptor of electronic doublets. Among the Lewis acidswhich may be used to complex the unsaturated imides, the alkylaluminiumdihalides such as the ethylaluminium dichloride and ethylaluminiumdibromide, the aluminium trihalides such as aluminium trichloride andaluminium tribromide, the boron halides such as boron trichloride, borontrifluoride etherate, the nickel halides such as nickel dichloride, maybe mentioned in a non limitative way. The compound acting as Lewis acidwith respect to the unsaturated imide is generally selected in such away that the complex it forms with the imide has a higher stability thanthat of the reaction products which the non-saturated imide may formwith the components of the coordination catalytic system used for thecopolymerization. The complex between the Lewis acid and the unsaturatedimide may be preformed before being introduced into the polymerizationarea, and for that purpose the said imide and the Lewis acid aredissolved in an inert solvent which may be the liquid used aspolymerization medium, maintained at a suitable temperature, e.g.between -80° C and +80° C. The complex may also be formed in situ in thepolymerization area before or during polymerization. The molarproportion of Lewis acid to be used to form the complex has to be atleast equal to the stoichiometric quantity and may reach four times thatquantity. Preferably the amount of Lewis acid used is such that themolar ratio of the Lewis acid to the unsaturated imide is between 1 to3.

Catalytic systems particularly suitable for preparing copolymersaccording to the invention are formed by the association of organiccompounds of aluminium with titanium, vanadium, tungsten or zirconiumderivatives, e.g. halides, oxyhalides, compounds in which at least oneof the valences of the transition metal is saturated by heteroatom,particularly oxygen or nitrogen, linked to an organic group such as theacetylacetonates, the benzoylacetonates and the alcoholates.

In some cases it may be advantageous to use a complex of the transitionmetal derivative with a ligand selected from the group comprising thealiphatic ethers such as diethyl and dipropyl ethers, diethoxyethane,the cyclic ethers such as tetrahydrofuran, dioxane, thioethers,phosphines, arsines, the tertiary amines such as trimethylamine,methyldiethylamine, the heterocyclic nitrogenous bases such as pyridine,quinoline, β-diketones, ketoesters, hydroxyaldehydes, aminoaldehydes,aminoalcohols.

It is particularly advantageous to use a catalytic system containing anorganoalumenum substance of formula:

    AlY.sub.q Cl.sub.(3-q),

where:

q is a number which may take the values 1, 3/2, 2 or 3, and

Y is a lower alkyl group such as ethyl, propyl, isobutyl, hexyl, saidorganoalumenum substance being associated to a titanium halide such asTiCl₄ or to a vanadium halide or oxyhalide such as VCl₄, VOCl₃ or tovanadium acetylacetonate. The said titanium or vanadium halides may becomplexed by tetrahydrofuran, an aliphatic ether, a tertiary amine,pyridine or quinoline.

The catalyst may possibly be deposited on a supporting medium orchemically bound to said supporting medium which may have an organic orinorganic nature.

The catalytic system may also contain a proportion of an activator whichmay particularly be an alkoxyalkyl halogenosulphite or halogenosulphate,such as ethoxyethyl chlorosulphite or chlorosulphate, ahalogenosulphonylthiophene such as di[chlorosulphonyl]-2,4-thiophene, ora dichloroarylphosphine such as the dichlorophenylphosphine.

In order to form the catalytic system the organometallic compound andthe compound of transition metal may be or may not be mixed togetherprior to being introduced into the polymerization area. The preformedcatalyst may be introduced into the polymerization area in a continuousor in an intermittent way.

The activator, if present, may be mixed to the catalyst before theintroduction into the polymerization area. The activator may also beadded directly to the mixture during polymerization, in a continuous wayor batchwise. With another operating method the activator is mixed firstwith the transition metal compound.

The catalytic system contains such amounts of organometallic compoundand of transition metal compound that the ratio of the number of metalatoms of the organometallic compound to the number of metal atoms of thetransition metal compound is between 1 and 50, and preferably between 2and 30.

The amount of activator may vary within wide limits. Particularly, from0.5 to 25 moles of activator may be used per transition metal atom butit is necessary that the polymerization medium contains moreorganometallic compound, expressed in metal atoms, than activatormolecules.

The liquid medium in which the copolymerization takes place mayadvantageously be an aliphatic, aromatic or cycloaliphatic hydrocarbonsolvent, particularly heptane, toluene, hexane, cyclohexane, benzene, ora mixture of such solvents. Inert halogenated hydrocarbons such aschloroform, chlorobenzene and tetrachloroethylene may also be used. Themono-olefins themselves may be used as the polymerization liquid mediumand the copolymerization may be carried out in the olefin or olefins tobe polymerized taken in the liquid state.

The preferred temperatures for carrying out the copolymerization rangefrom -30° C to +100° C. As to the pressures used for thecopolymerization, they may range, for example, from 1 to 50 atmospheres,or even more.

The complex between the unsaturated imide and the Lewis acid may beintroduced in its entirety into the polymerization area prior to theaddition of the catalytic system, or may be introduced into said areaduring the polymerization process in a continuous or discontinuous way.The amount of said complex in the polymerization medium relative to theamount of organometallic derivative of the catalytic system is notcritical and may be much higher than said amount of organometallicderivative.

The copolymerization may be carried out in a continuous way and, in thatcase, the liquid medium, the mono-olefins, the complexed nitrogenousunsaturated derivative and the possibly present non-conjugated diene, aswell as the catalytic system, are introduced in continuous operationinto a polymerization area with such flow rates that they dwell in saidarea during a sufficient period of time for ensuring that the desiredcopolymer concentration in the reaction mixture is obtained.

In carrying out the copolymerization process, any free oxygen iseliminated from the reaction medium, as well known in the art, bypassing an inert gas, particularly nitrogen, through said medium, priorto the polymerization.

The duration of the copolymerization process varies generally accordingto the operating conditions, and is most often comprised between 20minutes and 4 hours.

At the end of the operation the catalyst is destroyed in a well knownway, e.g. by adding an alcohol to the reaction mixture, then thecopolymer is separated from the solvent by coagulation by means ofaddition of an alcohol, by stripping off the solvent or by any othermethod enabling to separate a polymer from a solution in which it iscontained.

When the copolymers according to the invention are graft-copolymers,they result from the grafting of a suitable amount of one or more of theunsaturated imides giving the polar units on an amorphous statisticalcopolymer of the mono-olefins, or of the mono-olefins and thenon-conjugated diene or dienes, giving the non polar units.

The grafting method is not critical and any grafting method known in theart may be used to graft a vinyl monomer onto a copolymer of olefins orof olefins and non-conjugated dienes.

The graft copolymer may be advantageously prepared by the method whichcomprises the steps of dissolving the amorphous copolymer ofmono-olefins or of mono-olefins and non-conjugated dienes in a solvent,for example a solvent of the type used for the statisticalcopolymerization and particularly a hydrocarbon, adding a free radicalinitiator, particularly a peroxide such as benzoyl peroxide, thenraising the mixture obtained to the grafting temperature and maintainingit at said grafting temperature for a sufficient period of time to formactive sites on the amorphous copolymer, then adding the unsaturatedimide or imides in a suitable amount and allowing the substances presentto react at the grafting temperature in order to produce thegraft-copolymer.

The graft-copolymer may then be separated from the grafting reactionmedium by any known method and, for example, by washing the solution ofgraft-copolymer with a suitable solvent, preferably a solvent of thecorresponding monomer or homopolymers, then, after decantation, byprecipitation, by addition of an alcohol, of the graft-polymer containedin the organic phase particularly isopropanol. The separatedgraft-polymer is then oven-dried under low pressure.

Some of the copolymers according to the invention may be incorporated,in minor amounts, in a lubricating oil, possibly with other additives,to form improved lubricating compositions having a much better viscosityindex than the oil per se, as well as a satisfactory dispersing powerwith respect to the slurry (insoluble deposits) which may be formed inthe oil.

The copolymers according to the invention which are adapted to be usedas polymer additives for lubricating oils are copolymers containing, byweight, x% units derived from ethylene, y% units derived from amono-olefin having 3 to 6 carbon atoms or from a mono-olefin having 3 to6 carbon atoms and an non-conjugated diene, the proportion of unitsstemming from the diene being at most equal to 20% by weight, and z%units derived from one or more of the unsaturated imides previouslydefined, the values of x, y and z being such that 5 ≦ x ≦ 75, 5 ≦ y ≦85, and 0.1 ≦ z ≦ 20 with (x + y + z) = 100, said copolymers having alsoa reduced viscosity as measured in a solution at 0.1% in decalin at 135°C, comprised between 0.5 and 2, and a polydispersity lower than 5.

The reduced viscosity of the polymer additives, as measured in a 0.1%solution in decalin at 135° C, which may vary as previously indicatedfrom 0.5 to 2, is preferably comprised between 0.7 and 1.7.

As to the polydispersity of said additives, which has to be lower than5, it is preferably lower than 4, and more particularly between 2 and3.5.

It should be recalled that the polydispersity of a polymer is defined bythe value of the ratio of its weight average molecular weight M_(w) toits number average molecular weight M_(n).

A range of preferred polymer additives is formed by the terpolymers ofethylene and propene or butene-1 with one of the previously mentionedunsaturated imides, mainly one of the imides for which, in thehereinabove formula defining them, the alkenyl radical Z linked to thenitrogen atom is an alkenyl radical having 2 to 8 carbon atoms with,preferably, the unsaturation in the ω position relative to said nitrogenatom, said N-alkenylated imides being more particularly derived fromsuccinimide, glutarimide, phthalimide, maleimide, citraconic imides, theimide of himic anhydride, hexahydrophthalimide and the imide ofbutanetricarboxylic acid or of the esters of this acid.

For that range of preferred additives the ponderal proportions x, y andz of the units deriving respectively from ethylene, propene or butene-1,and from the unsaturated imide are preferably such that 20≦x≦75,20≦y≦75, and 0.10≦z≦15 with (x+y+z)=100.

When the copolymers according to the invention which may be used asadditives for lubricating oils are obtained by grafting a suitableamount of the above mentioned unsaturated imide or imides on anamorphous copolymer of ethylene with the mono-olefin having 3 to 6carbon atoms, mainly propene or butene-1, or with the mono-olefin having3 to 6 carbon atoms and the non-conjugated diene, said amorphouscopolymer used as a substrate has a reduced viscosity, as measured in a0.1% solution in decalin at 135° C, and a polydispersity comprised inthe ranges hereinabove defined; i.e. a reduced viscosity comprisedbetween 0.5 and 2, preferably comprised between 0.7 and 1.7, and also apolydispersity lower than 5, and more particularly a polydispersitybetween 2 and 3.5.

When preparing the polymer additive by statistical copolymerization orby grafting, it may be advantageous to operate in a solvent constitutedby an oil having the same composition as that of the oil to which theadditive has to be added, as it is not then necessary to isolate theadditive which can be collected in the form of a concentrated solutionin the oil used as the solvent.

The incorporation of the polymer additive to the lubricating oil may beperformed by any known method. In most cases, concentrated solutions ofadditives, called mother solutions, are prepared and diluted when usedto obtain the desired additive concentration in the lubricatingcomposition.

The concentration of the polymer additive in the lubricating compositionis generally of about 0.2 to 10%, and preferably 0.5 to 5% by weightwhen said lubricating composition is ready for use. However higherconcentrations, e.g. 15 to 30%, may be considered when the lubricatingcomposition has the form of a concentrate which is diluted in a suitableway when used.

The lubricating oils in which the polymer additive is incorporated toform the improved lubricating compositions may be natural or syntheticlubricating oils, or mixtures of such oils. As non-limitative examplesof such oils the following may be mentioned: vegetable oils such ascastor oil, ordinary or refined mineral oils of the paraffinic and/ormaphthenic type, hydrorefined oils, asphaltic oils, synthetic oils suchas the polybutenes or the alkylbenzenes such as dinonylbenzene andtetradecylbenzene, the alkyl and aryl ethers and/or esters ofpolyoxyalkylene such as ethers and/or esters of polyisopropyleneglycol,the esters or dicarboxylic acids and of various alcohols such as dibutyladipate and dioctyl phthalate, the so-called silicone oils such as, forexample, the polysiloxanes, the total or partial esters of thephosphoric acid, for example the tricresylphosphate and thealkylphosphoric acids.

In addition to the polymer additives according to the invention, thelubricating compositions may also contain other additives commonly usedin the art as corrosion inhibitors, antioxidants, dyes, defoamingagents.

The improved lubricating compositions containing the polymer additivesaccording to the invention may be used particularly as crank-case oilsfor internal combustion engines, as axle-case oils, as lubricants forgears or for the machining of metals, or also as lubricants fortwo-stroke engines.

The following examples will illustrate the invention; however they arenot to be construed as limiting its scope.

EXAMPLE 1

The copolymerization was carried out in a cylindrical reactor having acapacity of 6 liters, said reactor being provided with a stirrer, adropping funnel for introducing the unsaturated imide, two droppingfunnels for introducing the catalytic couple and tubes for the inlet andoutlet of gases. The reactor was immersed in a thermostatic bath and itstemperature was maintained during the entire copolymerization process at20° C.

The funnels above the reactor were purged and maintained under anitrogen atmosphere. 70 millimoles of a complex of N-vinylsuccinimideand ethylaluminium dichloride diluted in 100 millimoles of benzene wereintroduced into the bulb provided for introducing the unsaturated imide;said complex was prepared by mixing in benzene, at a temperature ofabout 10° C, N-vinylsuccinimide and ethylaluminium dichloride in a molarratio 1/1.

8 millimoles of vanadium tetrachloride (VCl₄) in 100 milliliters ofanhydrous heptane were introduced into one of the funnels provided forthe catalytic system, and 64 millimoles of ethylaluminium sesquichloridein 100 milliliters of anhydrous heptane were introduced into the otherone.

3.7 liters of heptane previously dried and degassed were introduced intothe reactor maintained under a nitrogen atmosphere. The flow of nitrogenwas stopped, then a mixture of ethylene and propene in a molar ratiopropene/ethylene equal to 1.2 was introduced through the gas inlet tube,said mixture circulating at a rate of 100 liters (normal) per hourduring the whole copolymerization.

Twenty minutes after beginning to introduce the gas mixture, thecomplexed unsaturated imide and the components of the catalytic systemwere injected drop by drop, the introduction of the monomer and that ofthe catalysts being carried out each in 100 minutes; then the injectionof the olefins is carried on for 10 minutes more. At the end of thereaction, an antioxidant was added to the reaction medium which is thensubsequently treated with water containing, by weight, 0.2%acetylacetone and 1% acetic acid.

138g of a statistical terpolymer was collected, in the form of anon-vulcanized elastomer which was amorphous as shown by X rayexamination, and which has a reduced viscosity (0.99), as measured in a1% solution in decalin 135° C, and a polydispersity of 3.

This terpolymer contained, by weight, 0.1% nitrogen, which correspondedto 0.9% units derived from the N-vinylsuccinimide, 43% units derivedfrom propene and 56.1% units derived from ethylene.

In order to study the effect of the polymer additive thus prepared onthe viscosity index (VI_(E)) of the lubricating oils, a determination ofthe viscosity index (VI_(E)) was made, according to the ASTM-D 2270standard, on a lubricating composition obtained by addition of 1.5% byweight of terpolymer to an oil referenced "200 Neutral" (neutralparaffin oil extracted by a solvent and having a viscosity of 44.1centistokes at 37.8° C, and of 6.3 centistokes at 98.9° C, and aviscosity index of 100).

For the purpose of comparison the determination has also been made ofthe viscosity index of a similar lubricating composition wherein theterpolymer according to the invention was replaced by the same amount ofa reference sample constituted by an amorphous copolymer of ethylene andpropene containing 54.4% by weight ethylene and having a reducedviscosity of 1.10 (as measured in decalin at 135° C), and apolydispersity of 3.

The viscosity index (VI_(E)) of an oil is a value based on aconventional scale, and characterizing the variation of the viscosity ofthe oil as a function of temperature; said index (VI_(E)) increases assaid variation decreases.

The results obtained are listed in Table I.

                  TABLE I                                                         ______________________________________                                                  "200 Neutral" oil + 1.5% additive                                             Viscosity at                                                                  37.8° C                                                                          98.9° C                                                      (cSt)     (cSt)       VI.sub.E                                      ______________________________________                                        Terpolymer  95.70       12.65       138                                       Reference sample                                                                          100.30      12.99       136.5                                     ______________________________________                                    

The incorporation of the terpolymer according to the invention in theabove mentioned lubricating oil considerably improves the viscosityindex of that oil. Moreover, a comparison between the results obtainedwith the terpolymer according to the invention and the reference samplecopolymer showed that the terpolymer had an influence on the viscosityindex which is higher than that of the reference sample copolymer.

The dispersing properties of the terpolymer according to the inventionand of the reference copolymer were evaluated by means of a test called"stain test method" which is carried out at 20° C and at 200° C,operating as follows:

Stain test at 20° C:

1.4g of a mother solution of polymer additive in a neutral oil of the"200 Neutral" type was poured into a flask of 60 ml, then was completedto 20g with a used oil containing about 2.4% slurry (insolubledeposits), the mixture obtained containing then 1.05% polymer additiveand 93% used oil. The said mixture was finely divided and homogenizedduring two minutes by means of a turbine rotating at 20,000 rpm, thetemperature of the mixture being about 50° C, then the thus preparedmixture was allowed to rest during 12 hours.

On a filter paper (Durieux® type n° 122) maintained completely flat, adrop of the mixture was then deposited by means of a calibrated glassrod (diameter 6 mm) placed 1 cm above the paper.

The stains were examined visually after 48 hours and were each given aqualification mark from 0 to 10 according to the following quotationscale:

    ______________________________________                                                        Qualification                                                 Dispersion      mark (base 10)                                                ______________________________________                                        Very good       9 to 10                                                       Good            7 to  8                                                       Poor to medium  4 to  6                                                       Null to very bad                                                                              0 to  1                                                       ______________________________________                                    

Stain at 200° C

The reference sample was prepared is the same way as that for the staintest at 20° C, and is also left resting for 12 hours.

2 cm³ of the sample was then taken off and put into a test tube whichwas immersed for 3 minutes in an oil bath at 200° C. A drop of thatsample oil was then immediately deposited on a filter paper in a mannersimilar to that described with reference to the stain test at 20° C, and48 hours later the stains are given a qualification mark according tothe visual examination scale indicated herein above.

The results obtained are listed on table II.

    ______________________________________                                                                   Qualification                                      Type of test                                                                              additive       mark (base 10)                                     ______________________________________                                        stain at  20° C                                                                    Terpolymer     8.5                                                            Reference copolymer                                                                          0.5                                                stain at 200° C                                                                    Terpolymer     8                                                              Reference copolymer                                                                          0                                                  ______________________________________                                    

The qualification mark resulting from the stain test at 20° C in thecase of the "200 Neutral" oil without polymer additive was 0.5.

EXAMPLE 2

A terpolymer according to the invention, which is adapted to be used asan additive for lubricating oils, was prepared by graftingN-vinylsuccinimide on a statistic copolymer of ethylene and propenehaving an ethylene content of 48% (by weight) and a reduced viscosity of1.57 (as measured in decalin at 135° C), a polydispersity of about 3 anda total ash content of 200 ppm.

In a reactor provided with a stirring device, having a capacity of 1liter and being maintained by thermostatic means at 93° C, 300 mlheptane and 12g of the ethylene/propene copolymer were introduced. 2mmoles of benzoyle peroxide was added and the resulting mixture washeated to 93° C and maintained at that temperature for 45 minutes. 0.35gN-vinylsuccinimide was then added and the temperature was maintained at93° C for 2 hours.

The hot solution was then washed with demineralised water and, afterdecantation, the polymer contained in the organic phase was precipitatedby means of isopropanol.

The graft copolymer obtained has a reduced viscosity of 1.14 (asmeasured in a 0.1% solution in decalin at 135° C) and aN-vinylsuccinimide content of 0.4% by weight.

In order to evaluate the effect of the graft terpolymer thus obtained onthe viscosity index of the lubricating oils, as well as its dispersingpower, a lubricating composition (oil + graft terpolymer) containing1.5% by weight of terpolymer, was prepared, starting from the referenceoil "200 Neutral", then the viscosity index (VI_(E)) of that compositionwas determined as well as its dispersing power due to the incorporationof the terpolymer as indicated in Example 1.

The viscosity at 37.8° C and 98.9° C of said composition wasrespectively 109.85 and 13.91 centistokes, which gave a viscosity index(VI_(E)) of 137.

As regards the dispersing effect, the qualification marks 7.2 and 6.8(base 10) according to the stain test method were found respectively at20° C and 200° C, which indicated a high dispersion capacity, and thus asatisfactory dispersing power of the graft terpolymer.

What is claimed is:
 1. A process for obtaining by coordination catalysisa substantially amorphous copolymer containing from 99.9 to about 80% byweight of non-polar units, 80 to 100% of said non-polar units derivedfrom two or more mono-olefins having the formula R--CH═CH₂ wherein R isa hydrogen atom or an alkyl radical having 1 to 16 carbon atoms and upto about 20% are derived from one or more non-conjugated diene selectedfrom the group consisting of 1,4-hexadiene, methyl-2-pentadiene,1,4-cyclopentadiene, 1,5-cyclooctadiene, tetrahydro-4,7,8,9-indene,bicyclo(3,2,0) heptadiene-2,6, dicyclopentadiene, andalkylidene-5-norbornene-2, and containing from 0.1 to 20% by weight ofpolar units derived from one or more cyclic imide having the formula##STR3## wherein Z is an alkenyl radical having 2 to 16 carbon atoms andwherein A is a hydrocarbon radical selected from the group consisting ofsaturated bivalent hydrocarbon radicals having 2 to 12 carbon atoms,unsaturated bivalent hydrocarbon radicals having 2 to 12 carbon atoms,amino, halogeno and carboxyl substituted bivalent unsaturatedhydrocarbon radicals having 2 to 12 carbon atoms which comprisescontacting, at a temperature from -80° C to 150° C, a member selectedfrom the group consisting of a mixture of two or more of saidmono-olefins, and a mixture of two or more of said mono-olefins with oneor more of said non-conjugated dienes, with one or more of saidunsaturated imides in the form of a complex formed with a Lewis acid, inthe presence of a catalytic system formed by the association of anorganometallic compound of one or more elements of the groups I, II andIII of the Mendeleev Periodic Table of the Elements with a compound of atransition metal of groups IV to VIII of said Periodic Table.
 2. Asubstantially amorphous copolymer prepared by the process of claim
 1. 3.A copolymer according to claim 2, wherein the N-alkenylated imides fromwhich are derived the polar units are such that the alkenyl radicalcontains 2 to 8 carbon atoms.
 4. A copolymer according to claim 2,wherein the N-alkenylated imides which cause the formation of the polarunits are derived from imides selected from the group consisting ofsuccinimide, glutarimide, maleimide, phthalimide, citraconic imide,hexahydrophthalimide, the imide of the himic anhydride and the imides ofthe tricarboxylic butane acid and the esters of said acid.
 5. Acopolymer according to claim 2, wherein the non polar units are derivedfrom ethylene and a mono-olefin having 3 to 6 carbon atoms or fromethylene, a mono-olefin having 3 to 6 carbon atoms and a non-conjugateddiene.
 6. A copolymer according to claim 2, wherein the non polar unitsare derived from ethylene and propene or from ethylene and butene-1. 7.A copolymer according to claim 5, containing, by weight, x% unitsderived from ethylene, y% units resulting from the mono-olefin having 3to 6 carbon atoms or from the mono-olefin having 3 to 6 carbon atoms andfrom the non-conjugated diene, and z% units derived from theN-alkenylated imide, the values of x, y and z being such that 5≦x≦75,5≦y≦85 and 0.1≦z≦20 with (x+y+z)=100, said copolymers further having areduced viscosity, as measured in a solution at 0.1% in decalin at 135°C, comprised between 0.5 and 2 and a polydispersity less than
 5. 8. Acopolymer according to claim 7, wherein said reduced viscosity isbetween 0.7 and 1.7.
 9. A copolymer according to claim 7, having apolydispersity less than
 4. 10. A copolymer according to claim 7,containing, by weight, x% units derived from ethylene, y% unitsresulting from propene or butene-1, and z% units derived from one ormore of the unsaturated imides, the values x, y and z being such that 20≦ x ≦ 75, 20 ≦ y ≦ 75, and 0.15 ≦ z ≦ 15, (x + y + z) being equal to100.
 11. A copolymer according to claim 2, wherein the catalytic systemused is formed by the association of an organoaluminic compound, or thecorresponding halogenated compound, and an vanadium halide or oxyhalide.12. A copolymer according to claim 2 wherein the copolymerization iscarried out in an inert liquid selected from the group consisting ofaliphatic, aromatic or cycloaliphatic hydrocarbons and the halogenatedderivatives of these hydrocarbons, at a temperature between -30° C and+100° C.
 13. A copolymer according to claim 3 wherein the N-alkenylatedimides from which are derived the polar units are such that the alkenylradical is unsaturated in the Omega position relative to the nitrogenatom to which it is linked.
 14. A copolymer according to claim 2 inwhich said alkylidene-5-norbornene-2 is methylene-5-norbornene-2 orethylidene-5-norbornene-2.
 15. A copolymer according to claim 2 whereinsaid alkylidene-5-norbornene-2 is ethylidene-5-norbornene-2.
 16. Acopolymer according to claim 7 having a polydispersity varying between 2and 3.5.